The present invention relates to an improved electronic immersion heater used particularly but not exclusively in aquariums or the like.
It is known that many of the fish species mostly cherished by aquarium owners need a very precise water temperature, since they come from tropical seas or in any case from regions with a very particular climate.
If water temperature is not kept at the ideal value within narrow limits, many of these fish species may become ill and often die.
A wide range of immersion heaters for aquariums is currently available; all, however, have a substantially identical basic structure.
Said basic structure comprises a tube, closed at one end, containing, in succession from the bottom towards the open end, a heating element, an electronic circuit board with the corresponding support and with a temperature sensor, and a hermetic plug.
The heating element is constituted by an electric resistor intermittently powered under the feedback control of the temperature sensor.
The aim of the temperature sensor is therefore to detect variations in water temperature in the aquarium and, if these temperature variations exceed certain preset limits, to drive the switch, closing or opening it and accordingly supplying power or not to the heating element.
The fundamental drawback of commercially available heaters resides in that the heating element produces such an amount of heat that, despite the dispersion provided by water and the thermal insulations provided inside the tube, the temperature sensor is affected by said heat.
In this manner, the temperature sensor does not measure the temperature conditions of the water but a combination thereof with the internal temperatures produced by the heater.
In order to obviate to this drawback it is possible to transfer the temperature sensor from the inside of the tube to the outside, connecting it to the electronic circuit board with a cable.
However, this solution has considerable practical drawbacks, the main ones being: the fragility of the component, which is no longer protected inside the tube, and the negative aesthetic impact caused by the presence of a dangling cable inside the aquarium.
Further attempts, keeping the temperature sensor inside the tube, have been made, trying in various ways to increase the interfacing between the sensor and the aquarium environment by means of the tube surface.
In this regard, the improved immersion heater for liquids disclosed in Italian patent application no. PD 93 A 000169 in the name of the same Applicant should be mentioned: the intermediary for contact between the sensor and the tube is an elastic lamina that is forced to copy the internal surface of said tube.
Although this solution improves the current technical situation, it is not free from drawbacks.
In particular, practical experience has demonstrated on one hand that not only the resistor, but also electronic components producing large amounts of heat influence the heat sensor, and on the other hand that the use of the lamina is not as effective as expected in theory, since in practice said lamina makes contact with the internal surface of the tube over very small areas.